|“||It's-it's nothing. At least, for now. This is the real way to move forward, Mum. To create a whole new world, your own world, without Father.||„|
|— Lucifer to Goddess|
in "The Good, the Bad and the Crispy"
The void is a place that exists outside of the known universe. It is beyond Earth, Heaven, Hell and outside the reach of God. Lucifer sent Goddess there so she could create a universe of her own. A few years later, God chose to retire to the universe that Goddess had created here after reconciling with his wife.
Lucifer used the Flaming Sword to cut through the boundaries of the universe created by Goddess and God, and formed a rift into a formless void, a place of nothingness much like the way our universe was in the beginning. He did so to give his mother a way to move forward, to begin again, to create a world of her very own, forever separated from her husband, as Lucifer saw that this was the only way to save his mother and prevent a war breaking out in Heaven that would kill many Angels.
Goddess agreed to Lucifer's plan and entered the void. After she had left, Lucifer removed The Key from the Flaming Sword and tossed The Blade of Death and The Medallion of Life into the void, so that the Flaming Sword could never be reassembled and the two universes would forever remain separate.
Three years later, Lucifer had Gabriel contact Goddess to reveal that God was retiring. Goddess managed to open a portal back, although it was stated that she only had enough power for just one trip between universes. Goddess revealed to have turned the Void into an entire universe of her own creation, noting that it wasn't as hard as her husband always claimed. God told Goddess that she's better at it than him if that's true and he was not surprised. God decides to retire with Goddess to her universe, stating that she had lived in his universe and it was time for him to live in hers. After saying goodbye Lucifer and Amenadiel, God and Goddess departed through the portal and into Goddess' universe.
Gabriel later tells Michael that "Mom's universe is pretty cool. The centaurs freak me out though." Gabriel reveals that while in Goddess' universe, she stole Azrael's Blade and the Medallion of Life for Michael.